Etching bath and method of etching



United States Patent M 3,337,462 ETCHING BATH AND METHOD OF ETCHING Clayton W. Hoornstra and John A. Easley, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Oct. 25, 1965, Ser. No. 505,190

7 Claims. (Cl. 252-79.4)

This application is a continuation-in-part of copending application Ser. No. 286,511, filed June 10, 1963, now abandoned.

This invention relates to an improved etching bath for powderless etching and the method of etching printing plates, name plates, templates and the like with the improved bath.

In the conventional method of making a metal printing surface, such as a photoengraving, a plate of an acid soluble metal such as magnesium, zinc or alloys having magnesium or zinc as the basis metal, is coated with a light-sensitive coating or enamel which is applied to the metal surface which is usually fiat or cylindrical. The coated surface is exposed to light through a negative having an image thereon so as to produce a corresponding image in the coating. The exposed coating surface is developed forming an acid resistant coating in the form of the image produced by the exposure. This acidresistant coating is further hardened by heating and the image-bearing surface of the plate is then subjected to etching by an acid. As the etching proceeds, the acid tends to etch laterally and undercut the resist and thus distort the image. The standard method of preventing or reducing this undercutting at one time was to powder the plate, a time-consuming and difficult operation. This method has now been replaced by the use of so-called powderless etching baths.

Heretofore, the powderless etching baths have generally employed as the principal ingredients (1) an etching agent consisting of nitric acid, (2) an organic, water-immiscible liquid and (3) a filming agent, in addition to (4) water. The filming agent employed in the prior art in powderless etching baths to reduce lateral etching or undercutting of the resist has most generally consisted of sulfated or sulfonated organic compounds that are surface active materials having both hydrophobic and hydrophilic properties.

Many of these sulfated or sulfonated compounds are not stable for long periods in an aqueous solution of strong mineral acid maintained at etching bath operating temperatures (50* to 120 B). One of the problems encountered in employing prior etching baths containing such filming agents has been the tendency for such baths to be 1) stable but incapable of etching combination plates in one step, or (2) capable of etching combination plates in one step but stable only for relatively short periods.

An object of the present invention is to provide stable etching baths which are suitable for etching combination plates.

It has now been discovered that an improved powderless etching bath may be formulated upon employing, as the filming agent, one or more compounds consisting of phosphorus-containing anionic surfactants selected from the group of compounds having the following formulas:

3,337,462 Patented Aug. 22, 1967 where R, R, R" and R' are each selected from the group consisting of hydrogen, alkali metal, alkaline earth metal, alkyl, alky1-O-CH aralkyl, aryl, aryloxyaryl, aryloxyalkyl, alkenyl, alky1(O-CH CH or alkyl-(O-CH CH -CH wherein x is an integer from 1 to 9 inclusive, and aryl-(OCH -CH or aryl-('O-CH CH CH wherein x is an integer from 1 to 9 inclusive, where at least one of R, R, R" or R is selected from the group consisting of alkyl, alkyl-O--CH aralkyl, aryl, aryloxyaryl, aryloxyalkyl, alkenyl, alkyl-(O-CH CH or wherein x is an integer from 1 to 9 inclusive, and

wherein x is an integer from 1 to 9 inclusive, and, where n is an integer from 2 to 10 inclusive, and mixtures thereof, and each of said alkyl, alkyl-OCH aralkyl, aryl, aryloxyaryl, aryloxyalkyl, alkenyl,

alkyl-(O-CH -CH or a1kyl-(O--CH CH -CH wherein x is an integer from 1 to 9 inclusive, and aryl-(OCH -CH or arylwherein x is an integer from 1 to 9 inclusive, groups containing from 6 to 18 carbon atoms, apart from oxymethylene, oxyethylene, oxypropylene, polyoxyethylene or polyoxypropylene groups and possessing solubility in both water and the organic, water-immiscible liquid employed.

The phosphorous-containing anionic surfactants employed in the present invention are further characterized as containing not more than 54 carbon atoms per molecular formula, apart from carbon atoms in oxymethylene, oxyethylene, oxypropylene, polyoxyethylene or polyoxypropylene groups or subgroups. Such compounds include orthophosphate, pyrophosphate, polyphosphate and phosphonate esters having as the organic radical or R group one of the following, or a combination of the same where more than one valence of the phosphate or phosphonate moiety is satisfied by an R group:

(1) Alkyl, e.g., (octyl) Na (P O disodium monooctyl orthophosphate, lauryl sodium pyrophosphate. (2) Alkenyl, e.g., oleyl sodium polyphosphate, decylenyl disodium orthophosphate, phosphated castor oil-sodium salt.

(3) Alkoxyalkyl and polyalkoxyalkyl, e.g., di-Z-ethylhexyloxyethylene disodium pyrophosphate, di-[Z-ethylhexyl(oxyethylene) disodium pyrophosphate, di- [lauryl(oxyethylene)4] Sodium orthophosphate, tri- [lauryl(oxyethylene) orthophosphate, di-(isobutoxyethyl) hydrogen orthophosphate.

(4) Alkoxyalkenyl and polyalkoxyalkenyl, e.g., linoleyl (oxyethylene) sodium orthophosphate.

(5) Aryl, e.g., monophenyl acid orthophosphate, di-

phenyl acid orthophosphate, disodium orthophosphate, diphenyl sodium orthophosphate. V

(6) Aryloxyaryl, e.g., phenoxyphenyl sodium polyphosphate.

(7) Aralkyl, e.g., benzyl sodium orthophosphate.

(8) Alkoxyaryl and polyalkoxyaryl, e.g., diphenyl(oxyethylene), sodium orthophosphate.

(9) Aryloxyarylalkoxy and aryloxyarylpolyalkoxy, e.g.,

phenoxyphenyl(oxyethylene) disodium orthophosphate.

3 Aralkyl, e.g., di-(dodecylphenyl) disodium pyrophosphate, ditolyl sodium orthophosphate. (11) Alkarylalkoxy and alkarylpolyalkoxy, e.g., nonylphenyl(oxyethylene) disodium orthiphosphate. (12) Fluoralkyl, e.g. H(CF CF -dihydrogen phosphonate.

Good etching results are obtained on plates, including combination plates, using a formulation containing such a filming agent and the formulation exhibits generally improved stability compared to prior known etching baths. Furthermore, there is the added flexibility that hydrochloric acid may be employed instead of nitric acid as the etching agent.

As indicated above, the improved bath of the invention employs as the filming agent, one or more or any of the phosphate ester anionic surfactants of the class described. A suitable proportion lies in the range of 0.3 to 10 percent by weight based on the total composition. A more preferred range is 0.5 to 3.5 percent by weight of filming agents.

Each of these compounds comprises one or more hydrophobic portions each consisting mainly of an alkyl or alkenyl or aryl group which tends to give the compound some solubility in the organic, water-immiscible liquid employed, and a hydrophilic portion consisting essentially of one of the following phosphate or phosphonate which tend to give the compound some solubility in water. Oxyethylene, oxypropylene, polyoxyethylene and polyoxypropylene sub-groups within R groups add further solubility in water. R groups as used here are those theoretically derived from ROH compounds which may individually consist of an adduct of an alkanol, aralkanol, phenol, phenyloxyalkanol, alkoxyphenol, or alkenol with from one to nine moles of ethylene oxide or propylene oxide per mole of the alcohol or phenol.

Each of these phosphate ester compounds, to be suitable, must exhibit a solubility in each of water and the organic, water-immiscible liquid of at least 0.01 percent by weight, as well as a solubility of at least 0.01 percent by weight in at least one of the water and the organic, Water-immiscible liquid. The water solubility at bath temperatures must not exceed about one percent by weight, however, since it is highly desirable that the preponderant amount of filming agent remains in the oil phase of the etching bath.

The phosphorated fatty alcohols, alkyl pyrophosphates, alkyl ethylene oxide pyrophosphates, alkyl propylene oxide pyrophosphates, alkyl orthophosphates, alkyl ethylene oxide orthophosphates, alkyl propylene oxide orthophosphates, arene orthophosphates, arene ethylene oxide orthophosphates, arene propylene oxide orthophosphates, alkyl polyphosphates, and phosphorated natural oils such as phosphorated castor oil, are more generally used.

Other natural oils which may be used in phosphorated form include tall oil, tung oil, cottonseed oil, linseed oil, palm oil, coconut oil, sperm oil, tallow, peanut oil, corn oil, and soya bean oil.

The phosphorated natural oils consist mainly of alkyl and alkenyl esters of the phosphate moiety in addition to unreacted glycerides, and, usually some of the phosphorus containing acid employed remains unreacted and present in the reaction product.

Other specific examples of suitable phosphate ester anionic surfactants and acid esters and salts of such esters include:

phosphorated castor oil, acid form;

dihydrogen octyl orthophosphate;

Z-ethylhexyl oxyethylene disodium orthophosphate;

2-ethylhexyl oxyethylene dihydrogen orthophosphate;

Z-ethylhexyl (oxyethylene) disodium orthophosphate;

2-ethylhexyl(oxyethylene) dihydrogen orthophosphate;

di-(2-ethylhexyl oxyethylene) sodium orthophosphate;

di-(2-ethylhexyl oxyethylene) hydrogen orthophosphate;

di-[Z-ethylhexyl(oxyethylene)2] sodium orthophosphate;

di [2-ethylhexyl( oxyethylene 2] hydrogen orthophosphate;

di-(2-ethylhexyl oxyethylene) dihydrogen pyrophosphate;

di- [Z-ethylhexyl (oxyethylene disodium pyrophosphate;

di- [Z-ethylhexyl (oxyethylene dihydrogen pyrophosphate;

pentacapryl pentasodium (P O phenyl dihydrogen orthophosphate;

phenyl sodium hydrogen orthophosphate;

diphenyl sodium orthophosphate;

di-(hexyl oxyethylene) disodium pyrophosphate;

di-(hexyl oxyethylene) dihydrogen pyrophosphate;

di-[hexyl('oxyethylene) disodium pyrophosphate;

di-[hexyl(oxyethylene) dihydrogen pyrophosphate;

di-(hexyl oxyethylene) sodium orthophosphate;

di-(hexyl oxyethylene) hydrogen orthophosphate;

hexyl oxyethylene disodium orthophosphate;

hexyl oxyethylene dihydrogen orthophosphate;

hexyl(oxyethylene) disodium orthophosphate;

hexyl(oxyethylene) dihydrogen orthophosphate;

isobutoxyethyl disodium orthophosphate;

isobutoxyethyl dihydrogen orthophosphate;

di-(isobutoxyethyl) sodium orthophosphate;

lauryl oxyethylene disodium orthophosphate;

lauryl oxyethylene dihydrogen orthophosphate;

di- [lauryl oxyethylene hydrogen orthophosphate;

phenyl(oxyethylene) disodium orthophosphate;

phenyl(oxyethylene) dihydrogen orthophosphate;

di- [phenyl (oxyethylene hydrogen orthophosphate;

phenyl(oxyethylene) disodium orthophosphate;

phenyl(oxethylene) dihydrogen orthophosphate;

di-[phenyl(oxyethylene) hydrogen orthophosphate;

nonylphenyl(oxyethylene) dihydrogen orthophosphate;

di-[pheny1(oxyethylene sodium orthophosphate;

di-[nonylphenyl(oxyethylene) sodium orthophosphate;

di- [nonylphenyl oxyethylene hydrogen orthophosphate;

oleyl disodium orthophosphate;

oleyl dihydrogen orthophosphote;

di-oleyl disodium pyrophosphate;

di-oleyl dihydrogen pyrophosphate; and

H(CF CF -P(O) (OH) 2 (fiuoroalkane phosphonate) where n is a number from 6-18.

Either hydrochloric acid or nitric acid may be employed as the etching agent. Operable concentrations of the acids are from 5-20 percent by volume of either 67 percent by weight nitric acid or 37.5 percent by weight hydrochloric acid, based on the total volume of the bath. A more preferred range of acid concentration is from 7-15 percent by volume of either 67 percent nitric acid or 37.5 percent hydrochloric acid based on the total volume of the bath.

The organic, water-immiscible liquid employed may be a single compound or a blend of such compounds. Required properties of this component are that it be substantially stable in the presence of dilute nitric acid or hydrochloric acid at bath temperatures, that it is a liquid at bath temperatures, and that it have some solvency for the phosphorus-containing filming agent, at least to the extent specified hereinabove. Substantially stable is defined as the non-occurrence of deterioration within a reasonable time period due to the presence of dilute nitric or hydrochloric acid which significantly alters the function of the organic, water-immiscible component within the path in an unfavorable manner.

The solvency properties of the organic, water-immiscible liquid are further defined by requiring that at least 50 percent by weight of such liquid consist of an organic solvent exhibiting a kauri-butanol (K.B.) test value of at least 70.

The term K.B. value as used herein refers to a known and used standard test for determining the solvent power value of a given organic liquid as the amount of that organic liquid which can be added to a standard kauri gum solution in butanol to produce a definite turbidity, as compared with the amount of pure benzene used as a standard in a similar titration and arbitrarily taken as 100 percent standard.

Examples of suitable organic solvents and their K.B. values are listed in the following table.

Organic solvent: K.B. value Panasol ANl solvent 1 106.2

Diisodecyl phthalate 68.7 Solvesso 150 liquid -4 83.4 Diamyl naphthalene 57.3 Panasol AN2 solvent 1 101.6 Hexyl acetate 203.0 Dibutyl phthalate 110.7 Diethyl phthalate 80.0 Dimethyl phthalate 37.6 Diethyl benzene 92 1 Panasol ANl and Pansol AN2 are each commercially available solvents consisting of more than 90 percent by volume of aromatic hydrocarbons and derivatives thereof.

By way of comparison, the normal K.B. value for mineral seal oil is about 25, while the value for White mineral oil is about 16.

The organic, water-immiscible liquid may consist entirely of one or more solvents having K.B. values about 70 or a blend of such solvents with other organic solvents, for example, aliphatics having lower K.B. values. It is highly desirable to avoid alcoholic solvents although up to percent of the organic, water-immiscible liquid required may consist of one or more alcohols.

Also, it is essential that this component is a liquid at bath temperatures. Suitable organic materials which can be used individually or in combination are hydrocarbon aromatics, and naphthenics boiling from 90 to 390 C. as, for example, diethyl benzenes, tetramethyl benzenes, diisopropyl benzenes and dodecyl benzenes. Other examples of water-immiscible liquids include turpentine, monochlorethyl benzene, ethylbutyl ketone, isophorone, methylhexyl ketone, di-limonene, diisodecyl phthalate, hexyla-cetate and the like. Generally, it may be said that water-immiscible esters, ketones, terpenes, ethers and aliphatic naphthenics and aromatic hydrocarbons are opera-ble.

Certain commercial solvents also serve very effectively as this component of the bath. An example is a commercial aromatic solvent, sold under the trade name of Solvesso 150 liquid, which is a mixture of approximately 90 percent alkyl benzenes, 2 percent naphthalene and 8 percent naphthenes. It has a flash point of 150 F. and an aniline point of -l8 F. and a distillation temperature range at 760 mm. Hg: initial boiling point of 303 F., 50 percent distilled at 378 F. and dry point at 415 F. Solvesso 150 has been replaced as a commercial product by Enco Aromatic 150 solvent which is nearly identical to Solvesso 150 and consists of about 97.3 percent by volume of total aromatics. Another commercial aromatic solvent employed has the trade name Penola H.A.N. and contains 84 percent aromatics, has a flash point of 140 F. and an aniline point of -2 F. and a distillation temperature range at 760 Hg: initial boiling point r 6 of 340 F., 50 percent distilled at 446 F. and dry point at 532 F.

The amounts of the water-immiscible, organic liquid employed may range from 1-10 percent by volume of the bath, but a preferred range is from 2-6 percent by volume based on the total volume of the bath.

In addition, small amounts of other modifying substances such as acetone or an unsaturated fatty acid, may be added to the bath, if desired, e.g., to change the filming properties of the filming agent, or, to change the solvency powers of the organic, water-immiscible liquid.

Suitable metals which may be etched by this process include zinc, zinc-base alloys, magnesium and magnesiumbase alloys, all of which are substantially homogeneous metals suitable for photoengraving. A zinc or magnesiumbase alloy is defined as having at least 70 percent of the base component.

To carry out the etching process, it is preferred to employ an etching machine of the type disclosed in U.S. Patent No. 2,669,048, issued Feb. 16, 1954. In this etchingmachine, rotating elongated paddles intermittently splash the etching bath upwardly against the image-bearing surface of the object being etched. The splashing action of the paddles also serves to keep the bath in a well emulsified state. A bath of this invention applied in the described manner for about 8 minutes will usually produce depths of etch from approximately 0.015 to .030 inch in line areas of the plate, while producing proper depths in various other parts of the plate. Generally an etching time of at least three minutes is needed to provide a well developed image. Also, etch factors in line image areas from 20-40 are readily obtainable. It is obviously desirable to have etch factors as high as possible for faithful reproduction of the image in relief. However, it should be noted that the etch factor can be sensitive to changes in depth. Thus, it should be considered as only one criterion of etching bath quality.

Each factor as used in this specification is defined as the ratio of the depth of the etch adjacent to a line of resist divided by one-half of the total loss in width (i.e., side etch) of metal immediately beneath the resist.

In an etching machine of the type described in the said patent and having 1.5 to 6 inch diameter paddles spaced from about 0.75 to 4 inches :below the plate to be etched, paddle speed may be varied from 300 to 1,000 revolutions per minute (r.p.m.), but more preferably, paddle speed is maintained in the range of 400 to 700 rpm. The average bath temperature may be within the range of from 50 to 120 F., but a more preferred range is from 50 to 100 F. and generally, temperatures from 70 to 90 F. optimize effectiveness and stability.

The following examples are intended to be merely illustrative of the invention and should not be construed as limiting the scope of the invention.

In a series of tests to demonstrate the advantages of the bath and method of the invention, there was employed a miniature etching machine of the type described in U.S. Patent No. 2,669,048. In each case, there was employed a photoengraving plate formed of a magnesium-base alloy having the nominal composition 3 percent of aluminum, 1 percent of zinc and the balance commercial magnesium. Each plate had developed thereon a photoresist image consisting of line areas and 65-screen half-tone areas, as well as blank areas. In each instance, before the plate was subjected to the action of the etching bath, the plate was descummed by brushing it with a 10 percent aqueous solution of nitric acid.

In each test, several photoengraving plates were etched during adjustment of the bath to the composition shown in the following examples. Thus, each bath was conditioned by prior use so that it contained amounts of the metal being etched.

Example 1.-An etching bath was prepared by placing in the etching machine 720 milliliters (ml.) of 67 percent aqueous nitric acid, 300 ml. of diethylbenzene and 180 grams of Victawet 58B, a composition containing at least 70 percent of a phosphorated higher alcohol having the formula (capryl) Na (P O and sufficient water to bring the total volume to 6 liters. A photoengraving plate prepared as described above was placed in the machine and etched in the foregoing bath for 6 minutes at 72 F. while employing a paddle speed of 600 r.p.m., the etching machine having 1% inch diameter paddles about 1 inch below the plate. The photoengraving plate was removed from the machine, rinsed, dried and examined. The relief depth was found to be 0.008 inch and side etch was 0.001 inch, giving an etch factor of 8.

Example 2.An etching bath was prepared by placing the following ingredients in an etching machine: 600 ml. of 67 percent nitric acid, 330 ml. of Solvesso 150 fluid, 60 grams of Zonyl S-lS fluoroalkyl phosphonate having the general formula where n has an average value of 3 to 4, and suflicient water to make a total volume of 6,375 ml. A photoengraving plate prepared as described above was placed in the machine and etched for 3 minutes at 74 F. while employing a paddle speed of 600 r.p.m. The photoengraving plate was removed from the machine, rinsed, dried and examined. The relief depth was 0.006 inch and side etch was 0.0007 inch, giving an etch factor of 8.

Example 3.An etching bath was prepared by placing the following ingredients in an etching machine: 600 ml. of 67 percent nitric acid, 120 ml. of n-hexylacetate, 150 grams of Victor Phosphated Castor Oil (neutralized), and sufficient water to make a total volume of 6,200 ml. A photoengraving plate prepared as described'above was placed in the etching machine and subjected to the action of the bath for 3 minutes at 74 F. with a paddle speed of 600 r.p.m. The photoengraving plate was removed from the machine and rinsed, dried and examined. The relief depth was found to be 0.0095 inch, while side etch was 0.0014 inch, giving an etch factor of 6.3.

Example 4.An etching bath was prepared by placing the following ingredients in an etching machine: 600 ml. of 67 percent nitric acid, 120 ml. of Solvesso 150 fluid, 180 grams of Chemsol 935-N organic polyphosphate, and suflicient water to make a total volume of 6,000 ml. A photoengraving plate prepared as described above was subjected to the action of the bath for 12 minutes at 100 F. with the paddle speed adjusted to 800 r.p.m. The pho' toengraving plate was then removed from the machine, rinsed, dried and examined. The relief depth was 0.0125 inch and side etch was 0.0004 inch, giving an etch factor of 31.

Example 5 .An etching bath was prepared by placing the following ingredients in an etching machine: 600 ml. of 67 percent nitric acid, 90 ml. of n-hexylacetate, 48 grams of Zelec NE fatty alcohol phosphate composition, and sufficient water to make a total volume of 6,040 ml. A photoengraving plate prepared as described above was placed in the machine, the machine was turned on and etching was carried out for 6 minutes at 72 F. with a paddle speed of 500 r.p.m. The photoengraving plate was then removed from the machine, rinsed, dried and examined. The relief depth was 0.008 inch while side etch was 0.0004 inch, giving an etch factor of 20.

A zinc micrometal alloy plate having the nominal composition of 99+% zinc with small amounts of magnesium and aluminum, and having a photoresist developed thereon, was descummed and placed in the etching machine and etched with this same bath for a period of 6 minutes at 72 F. with a paddle speed of 600 r.p.m. The zinc photoengraving plate was removed from the machine, rinsed, dried and examined. The relief depth was 0.007 inch and side etch was 0.0008 inch, giving an etch factor of 9.

Example 6.An etching bath was prepared by placing the following ingredients in an etching machine: 600 ml. of 67 percent nitric acid, 270 ml. of n-hexylacetate, 60 grams of Zelec NE fatty alcohol phosphate composition, 6 grams ricinoleic acid and sufiicient water to make a total volume of 6,000 ml. This bath was used to etch about a dozen small photoengraving plates to an average depth of 0.010 inch each during adjustment to the composition described. The bath was then allowed to stand overnight. A photoengraving plate of the type described above was then placed in the machine and the machine was turned on and etching was carried out for 8 minutes at 72 F. using a paddle speed of 800 r.p.m. The photo engraving plate was then removed from the etching machine, rinsed, dried and examined. The relief depth was 0.0155 inch and side etch was 0.0005 inch, giving an etch factor of 31.

Example 7.-An etching bath was prepared by placing the following ingredients in an etching machine: 600 ml. of 67 percent nitric acid, 240 ml. of Solvesso fluid, grams of Victawet 35B, a composition containing 70 percent of a phosphorated alcohol having the formula (octyl) Na (P O (where octyl=2-ethylhexyl), and sufficient water to make a total volume of 6,000 ml. A photoengraving plate prepared as described above was placed in the machine, the machine was turned on and etching was carried out for 10 minutes at 74 F. with a paddle speed of 600 r.p.m. The photoengraving plate was then removed from the machine, rinsed, dried and examined. The relief depth was 0.008 inch and the side etch was 0.0003 inch, giving an etch factor of 26.

Example 8.--An etching bath was prepared by placing the following ingredients in an etching machine: 700 ml. of 38 percent hydrochloric acid, ml. of Solvesso 150 fluid, 60 ml. of octyl acetate, 30 ml. of acetone, 120 grams of Victawet 35B composition containing at least 70 percent of phosphorated alcohol, and suflicient water to make a total volume of 6,300 ml. A photoengraving plate prepared as described above was placed in the etching machine. The machine was turned on and etching was carried out for 3 minutes at 75 F. with a paddle speed of 600 r.p.m. The photoengraving plate was then removed from the machine, rinsed, dried and examined. The relief depth was 0.008 inch and side etch was 0.0013 inch, giving an etch factor of 5.3

Example 9.An etching bath was prepared by placing the following ingredients in an etching machine: 700 ml. of 38 percent hydrochloric acid, 240 ml. of Solvesso 150 fluid, 30 ml. of acetone, 70 grams of phenyl acid phosphate, and suflicient water to make a total volume of 6,200 ml. A photoengraving plate prepared as described above was placed in the etching machine, the machine was turned on and etching was carried out for 6 minutes at 75 F. empolying a paddle speed of 600 r.p.m. The photoengraving plate was then removed from the machine, rinsed, dried and examined. The relief depth was 0.0125 inch and side etch was 0.001 inch, giving an etch factor of 12.5.

Example 10.-An etching bath was prepared by placing in the etching machine 600 ml. of 67 percent aqueous nitric acid, 210 ml. of Solvesso 150 fluid, 2.36 grams of Leyco 153 blended alkyl phosphates and suflicient water to bring the total volume to 6,210 ml. The alkyl of the alkyl phosphate blend used contained mainly from 6 to 18 carbon atoms. A photoengraving plate prepared as described above was placed in the machine and etched in the fore going bath for 8 minutes at 72 F. while employing a paddle speed of 600 r.p.m. The photoengraving plate was removed from the machine, rinsed, dried and examined. The relief depth was found to be 0.008 inch an side etch was 0.0005 inch, giving an etch factor of 16.

Example ]].An etching bath was prepared by plac ing in the etching machine 600 ml. of 67 percent aqueous nitric acid, 60 ml. of Solvesso 150 fluid, 200 grams of Barisol Super BRM (30% active) potassium salt of the phosphate of a complex multi-carbon alcohol, and suflicient water to bring the total volume to 6,060 ml. A photoengraving plate prepared as described above was placed in the machine and etched in the foregoing bath for 6'minutes at 72 F. while employing a paddle speed of 600 r.p.m. The photoengraving plate was removed from 5 the machine, rinsed, dried and examined. The relief depth was found to be 0.010 inch and side etch was 0.0008 inch, giving an etch factor of 12.5.

Exmnple'IZ-An etching bath was prepared by placing in the etching machine 900 ml. of 67 percent aqueous 10 nitric acid, 168 ml. of Penola heavy aromatic naphtha plus 42 ml. of diisodecyl phthalate, 84 grams of a mixture consisting substantially of -60 percent of a mixture of the diester of 2-ethylhexyl oxyethanol with pyrophosphoric acid and a minor amount of the diester of Z-ethylhexyl- (OCH CH OH with pyrophosphoric acid, 28 percent ofa mixture of the monoester of 2-ethylhexyl oxyethanol with orthophosphoric acid and a minor amount of the monoester of 2-ethylhexyl-(OCH CH OH with orthophosphoric acid, 10% unreacted Z-ethylhexyl oxyethanol and 2-ethylhexyl -(OCH -CH H and 2 percent phosphoric acids and sufficient water to bring the total volume to 6,210 ml. A photoengraving plate prepared as described above was placed in the machine and etched in the foregoing bath for 23 minutes at 7274 F. while employing a paddle speed of 700 rpm. The photoengraving plate was removed from the machine, rinsed, dried and examined. The relief depth was found to be 0.039 inch and side etch was from 0.0008 to 0.0012 inch, giving an etch factor of 50 to 33.

The foregoing described etching baths, on being compared to conventional, powderless etching baths, are found to exhibit excellent stability, producing favorable etching results over a 50 to 100 percent greater time period than for most conventional etching baths capable of use for etching combination plates.

Various modifications may be made in the etching bath and method of applying such bath without departing from the spirit of the invention, and it is to be understood that the scope of the invention is limited only by the appended claims as read in the light of the specification.

What is claimed is:

1. A powderless etching bath for etching a printing plate or photoengraving plate formed of zinc, zinc base alloy, magnesium or magnesium base alloy which comprises: 1) from to 20 percent by volume of an acid selected from the group consisting of nitric acid and hydrochloric acid; (2) from 1 to percent by volume of an organic, water-immiscible liquid, said organic, water-immiscible liquid being (a) substantially stable in the pres- 50 ence of the acid in the bath, (b) having not more than 10 percent by weight alcohol content based on the total weight of organic, Water-immiscible liquid in the bath, and (c) the organic, water-immiscible liquid consisting of at least 50 percent by weight of an organic liquid character- 55 ized by having a kauri-butanol test value greater than about 70; (3) from 0.3 to 10 percent by weight of a phosphate ester filming agent selected from the group of compounds having the following formulas:

O O (I) Roi -PoR" (II) R-o-1 o-i& oR"' J. a. R in 1'1 0 0 R 111)) RO1H-O-]l.l-OR' or (IV) RI|OH J) a. I i n LR" where R, R, R" and R are each selected from the group consisting of hydrogen, alkali metal, alkaline earth metal, alkyl, alkyl-OCH aralkyl, aryl, aryloxyaryl, aryloxyalkyl, alkenyl,

or alkyl-(O-CH --CH --CH wherein x is an integer from 1 to 9 inclusive, and

or ary1-(OCH --CH --CH wherein x is an integer from 1 to 9 inclusive,

where at least one of R, R, R" or R' is selected from the group consisting of alkyl, alkyl-OCH aralkyl, aryl, aryloxyaryl, aryloxyalkyl, alkenyl,

or alkyl-(OCH CH CH wherein x is an integer from 1 to 9 inclusive, and

or alkyl-(O-CH -CH -CH wherein x is an integer from 1 to 9 inclusive, and

aryl- (O-CHg-CHz) or aryl-(OCH CH CH wherein x is an integer from 1 to 9 inclusive, groups containing from 6 to 18 carbon atoms, apart from oxymethylene, oxyethylene, oxypropylene, polyoxyethylene or polyoxypropylene subgroups, said filming agent exhibiting a solubility of at least 0.01 percentin each of water and the organic, water-immiscible liquid; and (4) the balance being substantially water.

2. The composition as in claim 1 in which the phosphate ester filming agent is further characterized as containing not more than 54 carbon atoms per molecular formula, excepting carbon atoms in oxymethylene, oxyethylene, oxypropylene, polyoxyethylene'or polyoxypropylene groups or subgroups.

3. The composition as in claim 1 in which the phosphate ester filming agent is further characterized as having a solubility in water at bath temperatures not exceeding about one percent by weight.

4. The composition as in claim 1 in which the concentration of the phosphate ester filming agent-is in the range of 0.5 to 3.5 percent by weight.

5. The composition as in claim 1 in which the phosphate ester filming agent is selected from the group consisting of phosphorated fatty alcohol, alkyl pyrophosphate, alkyl ethylene oxide pyrophosphate, alkyl propylene oxide pyrophosphate, alkyl orthophosphate, alkyl ethylene oxide orthophosphate, alkyl propylene oxide orthophosphate, arene orthophosphate, arene ethylene oxide orthophosphate, arene propylene oxide orthophosphate, alkyl polyphosphate, alkyl phosphonate, phosphated natural oil, and mixtures thereof.

6. The method of etching the surface of an acid-soluble metal plate having an acid-resistant partial coating thereon, said metal being selected from the group consisting of magnesium, magnesium-base alloys, zinc and zinc-base alloys which comprises:

Providing an etching bath which comprises 1) from 5 to 20 percent by volume of an acid selected from the group consisting of nitric acid and hydrochloric acid, (2) from 1 to 10 percent by volume of an on ganic, water-immiscible liquid, said organic, waterimmiscible liquid being (a) substantially stable in the presence of the acid 'in the bath, (b) having not more than 10 percent by weight alcohol content based on the total weight of organic, water-immiscible liquid in the bath, and (c) the organic, water-immiscible liquid consisting of at least 50 percent by weight of an organic liquid characterized by having a kauributanol test value greater than about 70, (3) from (III) 0.3 to percent by weight of a phosphate ester filming agent selected from the group of compounds having the following formulas:

where R, R, R and R' are each selected from the group consisting of hydrogen, alkali metal, alkaline earth metal, alkyl, al-kyl-O-CH aralkyl, aryl, aryloxyaryl, aryloxyalkyl, alkenyl, alkyl-(O-CH 'CH or wherein x isan integer from 1 to 9 inclusive, and aryl-(O--CH CH or ary1-(O-CH CH CH wherein x is an integer from 1 to 9 inclusive and where n is an integer from 2 to 10 inclusive, but at least one of R, R, R or R' is selected from the group consisting of alkyl, alkyl-OCH aralkyl, aryl, aryloxyaryl, aryloxyalkyl, alkenyl, a1kyl-(O-CH CH or wherein x is an integer from 1 to 9 inclusive, and aryl-(O--CH CH or wherein x is an integer from 1 to 9 inclusive, and mixtures thereof,

12 and each of said alkyl, alky1-O-CH aralkyl,

aryl, aryloxyaryl, aryloxyalkyl, alkenyl,

5 or alkyl-(OCH CH CH wherein x is an integer from 1 to 9 inclusive, and

or aryl-(O-CH CH -CH wherein x is an integer from 1 to 9 inclusive, groups containing from 6 to 18 carbon atoms, apart from oxymethylene, oxyethylene, oxypropylene, polyoxyethylene or polyoxypropylene subgroups, said filming agent exhibiting a solubility of at least 0.01 percent in each of water and the organic water-immiscible liquid, but a solubility in water not exceeding about 1 percent by weight at bath temperature, and (4) the balance substantially water; bringing the etching bath to a well emulsified condi- 20 tion;

and impinging the etching bath upon the metal surface to be etched. 7. The method of claim 6 wherein the bath is maintained at a temperature within the range of from about 50 to 120 F. and impinging of the bath upon the acid soluble metal is carried out for a period of at least 3 minutes.

References Cited UNITED STATES PATENTS 1,913,545 7/1933 Doy 2s2 79.2 XR 2,559,754 7/1951 Bittles 252147 3,004,879 10/ 1961 Whitby 25279.4 XR 3,074,836 1/1963 Sherer et al 25279.4 XR 3,232,884 2/1966 Lemaire et al. 25279.4

OTHER REFERENCES Zonyl, S-l5 Fluorochemical Surfactant, Du Pont Dyes and Chemicals Information Bulletin, 1960, p. 3.

LEON D. ROSDOL, Primary Examiner.

M. WEINBLATT, Examiner. 

1. A POWDERLESS ETCHING BATH FOR ETCHING A PRINTING PLATE OR PHOTOENGRAVING PLATE FORMED OF ZINC, ZINC BASE ALLOY, MAGNESIUM OR MAGNESIUM BASE ALLOY WHICH COMPRISES: (1) FROM 5 TO 20 PERCENT BY VOLUME OF AN ACID SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID AND HYDROCHLORIC ACID; (2) FROM 1 TO 10 PERCENT BY VOLUME OF AN ORGANIC, WATER-IMMISCIBLE LIQUID, SAID ORGANIC, WATER-IMMISCIBLE LIQUID BEING (A) SUBSTANTIALLY STABLE IN THE PRESENCE OF THE ACID IN THE BATH, (B) HAVING NOT MORE THAN 10 PERCENT BY WEIGHT ALCOHOL CONTENT BASED ON THE TOTAL WEIGHT OF ORGANIC, WATER-IMMISCIBLE LIQUID IN THE BATH, AND (C) THE ORGANIC, WATER-IMMISCIBLE LIQUID CONSISTING OF AT LEAST 50 PERCENT BY WEIGHT OF AN ORGANIC LIQUID CHARACTERIZED BY HAVING A KAURI-BUTANOL TEST VALUE GREATER THAN ABOUT 73; (3) FOR 0.3 TO 10 PERCENT BY WEIGHT OF A PHOSPHATE ESTER FILMING AGENT SELECTED FROM THE GROUP OF COMPOUNDS HAVING THE FOLLOWING FORMULAS: 